The methylation of the C-terminal region of hnRNPQ (NSAP1) is important for its nuclear localization

Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, Campinas, SP, Brazil.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 08/2006; 346(2):517-25. DOI: 10.1016/j.bbrc.2006.05.152
Source: PubMed


Protein arginine methylation is an irreversible post-translational protein modification catalyzed by a family of at least nine different enzymes entitled PRMTs (protein arginine methyl transferases). Although PRMT1 is responsible for 85% of the protein methylation in human cells, its substrate spectrum has not yet been fully characterized nor are the functional consequences of methylation for the protein substrates well understood. Therefore, we set out to employ the yeast two-hybrid system in order to identify new substrate proteins for human PRMT1. We were able to identify nine different PRMT1 interacting proteins involved in different aspects of RNA metabolism, five of which had been previously described either as substrates for PRMT1 or as functionally associated with PRMT1. Among the four new identified possible protein substrates was hnRNPQ3 (NSAP1), a protein whose function has been implicated in diverse steps of mRNA maturation, including splicing, editing, and degradation. By in vitro methylation assays we were able to show that hnRNPQ3 is a substrate for PRMT1 and that its C-terminal RGG box domain is the sole target for methylation. By further studies with the inhibitor of methylation Adox we provide evidence that hnRNPQ1-3 are methylated in vivo. Finally, we demonstrate by immunofluorescence analysis of HeLa cells that the methylation of hnRNPQ is important for its nuclear localization, since Adox treatment causes its re-distribution from the nucleus to the cytoplasm.

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Available from: Alexandre J C Quaresma
    • "hnRNP Q has been previously shown to be methylated in vitro by PRMT1 and its in vivo methylation is important for its nuclear localization [26] and for insulin receptor trafficking and insulin signalling [27]. The small nuclear ribonucleoprotein B and B1 (snRNPB), which is involved in several steps of the biogenesis of the snRNPs, has also been found methylated on arginine residues but the PRMT responsible for this modification has not been identified yet [28]. "
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    ABSTRACT: PRMT6 is a protein arginine methyltransferase that has been implicated in transcriptional regulation, DNA repair, and human immunodeficiency virus pathogenesis. Only few substrates of this enzyme are known and therefore its cellular role is not well understood. To identify in an unbiased manner substrates and potential regulators of PRMT6 we have used a yeast two-hybrid approach. We identified 36 new putative partners for PRMT6 and we validated the interaction in vivo for 7 of them. In addition, using in vitro methylation assay we identified 4 new substrates for PRMT6, extending the involvement of this enzyme to other cellular processes beyond its well-established role in gene expression regulation. Holistic approaches create molecular connections that allow to test functional hypotheses. The assembly of PRMT6 protein network allowed us to formulate functional hypotheses which led to the discovery of new molecular partners for the architectural transcription factor HMGA1a, a known substrate for PRMT6, and to provide evidences for a modulatory role of HMGA1a on the methyltransferase activity of PRMT6.
    No preview · Article · Nov 2013 · PLoS ONE
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    • "In mammalian cells, arginine methylation facilitates nuclear import or slowing of nuclear export of these hnRNPs. This role is supported by the observation that the suppression, in the cases of hnRNP A2 and Q, of arginine methylation leads to a shift from predominately nuclear localization to predominately cytoplasmic localization [46] [47] [53]. Treatment with the methyltransferase inhibitor adenosine dialdehyde (AdOx) resulted in increased cytoplasmic localization of Src substrate-associated during mitosis (Sam68), an RNA-binding protein that belongs to the hnRNP K homology (KH) domain family [54]. "
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    ABSTRACT: In eukaryotes, messenger RNA biogenesis depends on the ordered and precise assembly of a nuclear messenger ribonucleoprotein particle (mRNP) during transcription. This process requires a well-orchestrated and dynamic sequence of molecular recognition events by specific RNA-binding proteins. Arginine methylation is a posttranslational modification found in a plethora of RNA-binding proteins responsible for mRNP biogenesis. These RNA-binding proteins include both heterogeneous nuclear ribonucleoproteins (hnRNPs) and serine/arginine-rich (SR) proteins. In this paper, I discuss the mechanisms of action by which arginine methylation modulates various facets of mRNP biogenesis, and how the collective consequences of this modification impart the specificity required to generate a mature, translational- and export-competent mRNP.
    Full-text · Article · Apr 2011
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    • "However, it was also identified in cytoplasmic granules that consist of large complexes of mRNA-binding proteins, which may be transported by cellular motors, such as proteins of the kinesin superfamily (KIFs) [52]. Furthermore, both, lack of arginine methylation by PRMT and tyrosine specific phosphorylation by insulin receptor can promote its re-distribution from the nucleus to the cytoplasm [14] [20]. Fig. 2 "
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    ABSTRACT: Eukaryotic gene expression is regulated on different levels ranging from pre-mRNA processing to translation. One of the most characterized families of RNA-binding proteins is the group of hnRNPs: heterogenous nuclear ribonucleoproteins. Members of this protein family play important roles in gene expression control and mRNAs metabolism. In the cytoplasm, several hnRNPs proteins are involved in RNA-related processes and they can be frequently found in two specialized structures, known as GW-bodies (GWbs), previously known as processing bodies: PBs, and stress granules, which may be formed in response to specific stimuli. GWbs have been early reported to be involved in the mRNA decay process, acting as a site of mRNA degradation. In a similar way, stress granules (SGs) have been described as cytoplasmic aggregates, which contain accumulated mRNAs in cells under stress conditions and present reduced or inhibited translation. Here, we characterized the hnRNP Q localization after different stress conditions. hnRNP Q is a predominantly nuclear protein that exhibits a modular organization and several RNA-related functions. Our data suggest that the nuclear localization of hnRNP Q might be modified after different treatments, such as: PMA, thapsigargin, arsenite and heat shock. Under different stress conditions, hnRNP Q can fully co-localize with the endoplasmatic reticulum specific chaperone, BiP. However, under stress, this protein only co-localizes partially with the proteins: GW182-GWbs marker protein and TIA-1 stress granule component.
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